The present invention relates to pistons for reciprocating machines for example internal combustion engines or pumps.
In a conventional internal combustion engine one or more pistons are slidingly located in cylinder bores and are sealed with respect thereto by means of piston rings. The piston rings engage in circumferential grooves in the wall of the piston, adjacent the piston head. The rings which are split, are made of resilient metal and in their relaxed state are of greater diameter than the cylinder bore, so that they will engage in the cylinder bore under compression. In order to accommodate manufacturing tolerances and expansion, when engaged in the cylinder bore, a gap remains between the ends of the piston rings.
With such piston rings, a single ring will provide about 95% sealing, the main leakage occurring through the gap between the ends of the ring, a second ring is required to minimize this leakage.
Both piston rings contribute significantly to the frictional forces of the engine. The present invention avoids the need for a second piston ring thus reducing the frictional losses of the engine.